1. Field of the Invention
The present invention relates to a method of manufacturing a thermoplastic resin sheet having a laminated structure and an apparatus therefor, and an obtained sheet can be used for packaging food products, medical and pharmaceutical products and the like.
2. Description of the Related Art
A laminated thermoplastic resin sheet, obtained by laminating a function film which applies an easy slipping characteristic, an oxygen barrier characteristic and the like to a base material sheet made of a polypropylene or the like, is used in a field of food products and the like.
The easily slipping film includes a nonoriented polypropylene film and the like, and the oxygen barrier film includes an EVOH film and the like.
Conventionally, such a laminated thermoplastic resin sheet is manufactured by a coextrusion method, a dry laminate method or the like.
However, in the case of the coextrusion method, since an adhesive layer having a certain thickness or more is required between the base material sheet and the function film, the adhesive layer prevents a transparency. Further, it is hard to manufacture a multiple layer sheet made of resins having different melting characteristics with increasing transparency. Still further, since a rate of an edge portion of the sheet to be trimmed is relatively large, a cost loss is increased in the case that the function film is expensive such as the EVOH film.
On the contrary, in the case of the dry laminate method, since the sheet and the film are bonded to each other through an adhesive, an amount of the adhesive is increased, so that cost is increased, when the thickness of the sheet becomes thick due to an increase in the number of the layers. Since a solvent is contained in the adhesive, a countermeasure for the environment is necessary.
Accordingly, an object of the present invention is to provide a method of manufacturing a laminated thermoplastic resin sheet having an improved transparency without generating a wrinkles and an apparatus therefor.
In accordance with a first aspect of the present invention, there is provided a method of manufacturing a laminated thermoplastic resin sheet, which uses a manufacturing apparatus comprising a first cooling roll having a surface coated by an elastic material, a second roll, a metal endless belt wound between the first roll and the second roll and a third cooling roll, brought into contact with the first cooling roll through the metal endless belt, comprising the steps of arranging a guide roll for introducing a film near the first or third roll so as to introduce a thermoplastic resin sheet in a melting state between the first and third cooling rolls in such a manner as to be brought into contact with the metal endless belt supported by the first cooling roll and the third cooling roll substantially at the same time, introducing a thermoplastic resin film between the metal endless belt and the third cooling roll through the guide roll so as to laminate the sheet and the film, pressing and cooling the laminated thermoplastic resin sheet in a plane manner by the first and third rolls while elastically deforming the elastic material by a pressing force between the first and third rolls, and continuously pressing and cooling the laminated thermoplastic resin sheet to the third cooling roll in a plane manner by the endless belt.
In accordance with the present invention, it is preferable that the metal endless belt and the rolls are formed in a mirror surface having a surface roughness 0.5 S or less.
A stainless steel, a carbon steel, a titanium alloy and the like can be used for a material of the metal endless belt. A thickness of the endless belt can be optionally selected, however, from the view point of the belt strength, e.g. 0.3 mm or more is preferable.
In this case, it is sufficient that at least the first cooling roll and the second roll are situated at the inside of the endless belt, and the other tolls for adjusting a tension and for cooling in an auxiliary manner may be included.
A fluorine rubber, a silicone rubber, an EPDM, an NBR and the like can be used for the elastic material. Further, it is preferable to set a thickness of the elastic material to be 3 mm or more for obtaining an improved plane pressure by an elastic deformation.
The thermoplastic resin sheet in the melting state corresponds to, for example, a thermoplastic resin sheet immediately after being extruded from a T die of an extruding machine.
The thermoplastic resin sheet becomes a base material sheet, and a material thereof can be optionally selected among a polyethylene, a polypropylene, a polystyrene, a nylon and the like.
The thermoplastic resin film corresponds to, for example, a formed film fed out from a film supply roll. The thermoplastic resin film corresponds to a function film applying functions such as an easy slipping characteristic, an oxygen barrier characteristic and the like to the base material sheet. For example, in the case of the easily slipping film, a non oriented polypropylene film or the like is employed, and in the case of the oxygen barrier film, an EVOH film is employed.
The thermoplastic film may have a multiple layer structure, for example, a two layer structure comprising EVOH layer/PP layer, and a three layer structure comprising PP layer/EVOH layer/PP layer.
A thickness of the thermoplastic resin film can be optionally selected,.however, 10 to 1000 xcexcm is preferable. Cooling means may be provided in the first to third rolls.
In the present invention, since the thermoplastic resin sheet and film are relatively different from each other only in view of a thickness, any of them may be called as the sheet or the film.
In accordance with the present invention, the sheet and the film are pressed and laminated in a plane manner together with an elastic deformation of the elastic material, a bonding strength between the laminated sheets is improved, and a rate of shrinkage at a time of laminating can be controlled within a certain small range.
Further, at a time of laminating the sheet and the film, since the guide roll for introducing the film is arranged near the first or third roll, the film is brought into a little contact with the endless belt or the third roll, so that the thermoplastic resin film can be prevented from generating a wrinkle as much as possible.
In accordance with a second aspect of the present invention, there is provided a method of manufacturing a laminated thermoplastic resin sheet as recited in the first aspect, wherein the guide roll for introducing the film is arranged at a position at which an angle formed by a line between both centers of the first and third rolls and a contact point of the thermoplastic resin film with the endless belt or the third roll is 45 degrees or less.
When the contact portion between the thermoplastic resin film and the endless belt or the third roll is increased, a generation of the wrinkle is increased at the degree, so that the angle is set to be 45 degrees or less in order to prevent wrinkling this as much as possible. The angle is preferably 30 degrees or less.
The object to be contacted is set to the endless belt or the third roll for the reason of corresponding to the case that the thermoplastic resin film is laminated on one surface (a front surface) or another surface (a back surface) of the thermoplastic resin sheet.
Here, in the present invention, a definition is made by the angle formed by a line between both centers of the first and third rolls and the contact point of the thermoplastic resin film with the endless belt or the third roll, however, a definition may be made by an introducing angle of the thermoplastic resin film to a nip portion (between the first and third cooling rolls) with respect to the line between both centers of the first and third rolls, and it is preferable as the angle is near 90 degrees.
In accordance with a third aspect of the present invention, there is provided a method of manufacturing a laminated thermoplastic resin sheet as stated in the first or second aspect, wherein a back tension 9.8 N/m to 294.0 N/m is applied to the thermoplastic resin film.
The back tension can be applied by adjusting a speed of a supply device for the thermoplastic resin film.
In the case that the back tension is less than 9.8 N/m, an effect of sufficiently preventing a generation of a wrinkle and an effect of improving a stability in manufacturing can not be obtained. Further, when it is more than 294.0 N/m, there is a risk that the thermoplastic resin film extends so that a width of the film is narrowed.
In accordance with a fourth aspect of the present invention, there is provided a method of manufacturing a laminated thermoplastic resin sheet as stated in any one of the first to third inventions, wherein the thermoplastic resin film is laminated on either the one surface or another surface of the molten thermoplastic resin sheet through the guide roll for introducing the film.
That is, in accordance with the present invention, there can be obtained a laminated thermoplastic resin sheet structured to have at least three layers in which thermoplastic resin films are respectively laminated on an upper layer and a lower layer of the thermoplastic resin sheet as an intermediate layer.
In accordance with a fifth aspect of the present invention, there is provided an apparatus for manufacturing a laminated thermoplastic resin sheet, comprising a first cooling roll having a surface coated by an elastic material, a second roll, a metal endless belt wound between the first roll and the second roll, a third cooling roll brought into contact with the first cooling roll through the metal endless belt, molten resin supplying means arranged so as to introduce a thermoplastic resin sheet in a melting state between the first and third cooling rolls in such a manner as to be brought into contact with the metal endless belt contact with the first cooling roll and the third cooling roll substantially at the same time, and a guide roll for introducing the film arranged near the first or third roll so as to introduce a thermoplastic resin film between the metal endless belt and the third cooling roll.
The present invention corresponds to an apparatus for realizing the first method discussed above.
In accordance with a sixth aspect of the present invention, there is provided an apparatus for manufacturing a laminated thermoplastic resin sheet as recited in the fifth aspect, wherein the guide roll for introducing the film is arranged at a position at which an angle formed by a line between both centers of the first and third rolls and a contact point of the thermoplastic resin film with the endless belt or the third roll is 45 degrees or less.
The present invention corresponds to an apparatus for realizing the second method discussed above.
In accordance with a seventh aspect of the present invention, there is provided an apparatus for manufacturing a laminated thermoplastic resin sheet as recited in the fifth or sixth aspect, wherein the guide roll for introducing the film is arranged in either one surface or another surface of the molten thermoplastic resin sheet.
The present invention corresponds to an apparatus for realizing the fourth method discussed above.